A break in a coastline or a passage between shoals, and so forth.

1. A widening of a crevice, in consequence of a softening or decomposition of the adjacent rock, so as to leave a vacant space.

2. A short heading driven between two or more parallel headings or levels for ventilation.

3. An area in a coal mine between pillars, or between pillars and ribs.

Any break in sea ice which reveals the water.